Electrolytic condenser



Patented Nov. 1o, 1936 UNITED STATI-:s`

PATENT .OFFICE 2,060,022 ELECTROLYTIC CONDENSER Joseph B.v Brennan, Fort Wayne. Ind. Y

' such as electrolytic condensers, rectiiiers, or

lightning arresters of the type embodying an anode having a dielectric film thereon and a cathode on which no film'is formed.

In devices -of this characterythe container for holding the electrolyte ordinarily is the cathode and frequently comprises an aluminum can provided with means for connection into the elec-` trical circuit. Aluminum cans 'are desirable from the standpoint of appearance, and also befcause they can be produced very cheaply by an extrusion method. However, when such cans are used as cathodes in electrolytic condensers, the electrolyte ordinarily employed has a corrosive effect on the aluminum and it has been necessary heretofore to protect the aluminum by chromium plating the inside of the cans. This process is not only expensive but also has the effect of slightly increasing the resistance of the condenser.

It is among the objects of my invention to provide a method for protecting the internal surfaces of containers and cathodes for electrolytic devices, which can be carried out-economically and expeditiously. Another object is to provide a protecting surface for the internal surfaces of containers and cathodes for electrolytic devices which can beproduced economically and which will afford permanent protection, A further object is to' provide a cathode for electrolytic condensers which will reduce the resistance of the condenser as compared to previous practices,

Briefly, I attain the objects outlined above vby 'spraying or otherwise coating the surface of the cathode exposed to the electrolyte with finely divided molten copper or other suitable metal, thus producing a roughened, somewhat porous surface of protecting metal, which surface is conductive throughout its area. Further objects and advantageous features of my invention will become apparent from the fol- 'lowing description of a preferred form thereof, reference being made to theaccompanying drawing in .which Figure 1 is a cross section through a condenser made according to my invention; and Figure 2 diagrammatically illustrates a method of spraying the inside of the containers.

Referring to the drawing in which my inven tion is illustrated in conjunction with a 'well known type of electrolytic condenser, the reference character il indicates the container in general. This comprises the cathode of the condenser and also the container for the electrolyte Il. The container is closed by any suitable cap member i 2, and if desired the cap may be provided with a vent to allow the escape of gases generated within the condenser. At its lower end, the container is provided with a threaded neck portion I3 which serves as an electrical 5 terminal for the cathode and which is hollow to permit passage of the terminal I4 for the anode i 5. The terminal is insulated from the neck portionby a, rubber sleeve i6, and'a fiuid tight joint'is produced by crimping lin the projecting 10 sleeve |11 to Acompress the rubber insulation against the terminal member i4. The anode i5 comprises a, cylinder or tube of film-forming material having a dielectric film suitably formed thereon, and preferably the anode is constructed 15 according to the disclosure of my application' Serial No. 662,107, filed March 22, 1933, in which I disclose an anode having a conductive surface of finely divided film formi/ng material sprayed thereon, whereby the capacity of the anode 'is 20 greatly increased. In order to protect the aluminum cathode and container I0 from the corrosive action of the lelectrolyte Ii I cover the internal surfaces thereof with a layer of finely divided particles of copper indicated by 20. The copper is sprayed into the container` in a molten condition by an atom-` izing gun with the result that the minute particles of molten copper adhere to the interior surface of the aluminum can and effectively protect it against the corrosive action of the electrolyte. Furthermore, each particle of `copper apparently makes electrical contact with an adjacent particle or particles, so that the entire surface is 'conductive throughout. Because of 35 the finely divided condition of the copper, the area of copper actually in contact with the electrolyte is ,increased greatly as compared to the area oi' the container itself. By reason of this great increase in area, the resistance to flow of 40 current between the electrolyte and the cathode is greatly reduced, and likewise the current density per unit of area of the cathode actually in contactwith the electrolyte is reduced and thus destructive arcing and heating up of the cathode and electrolyte is eliminated. 'I'he coating is somewhat porous so that the electrolyte may permeatetherethrough, butit nevertheless effectively protects the aluminum can against corrosion. i

In Figure 2,- I have illustrated diagrammatically the method and apparatus which I preferably employ to form the porous layer on the inside of the container.- This comprises a spray gun G y having a head 2t to which oxygen and acetylene 55 corrode.

or other suitable gases may be supplied through pas gges 24 and 2l extending through the handle of e-gun and terminating in a mixing chamber 2s. The copper or other suitable metal is supplied by a wire W which is fed into the center of the mixing chamber by feeding mechanism 21.

'I'he metal is melted by the acetylene flame and atomized by a blast `of compressed air `or other suitable gas supplied to the annular chamber 2l through the passageway Il. The atomized metal is directed into the container to deposit the protective nlm or layer thereon and the gun may be manipulated by hand to produce an even deposit of the desired thickness. I have obtained good results by using an oxy-acetylene flame to fuse 4a copper wire and by employing a blast of compressed air at about lbs. pressure per square inch to atomize the molten metal. The gun is preferably held close to the entrance or opening of the container so that the copper is quite hot when it impinges on the surface of the aluminum and thus a rather dense deposit is formed. If desired, the passageway in the neck I3 may be protected from the molten copper by a plug Il,

and a shield Il may be used to prevent copper from striking the outside of `the container and marring its appearance. Y

This method causes the molten or plastic particles of metal to impinge upon the interior of the container with sufficient force to adhere thereto and to cohere yto each other. The layer of deposited metal' is apparently ,Y conductive throughout and seems to besomewhat' porous and microscopically honey-combed. roughened, and reticulated throughout. The electrolyte is thus able to penetrateI the surface and accdingly the area of contact between the electrolyte and the conductive cathode layer is very large. I prefer to coat th'e entire inner surface of the cathode, but this is not essential as corrosion will be sub stantially prevented by a relatively small area of copper, for the copper has'mgreater tendency to go into solution than aluminum. l

Fromlthe foregoing description of a preferred formtof my invention, it will bel seen that I have provided `a lcontainer for electrolyticr devices which can be produced cheaply and rapidly with a small capital investment and which will not condensers embodying my containers or cathodes have a lower resistance than prior types of condensers and are free from troubles caused by arcing between the electrolyte and cathode.

.While I have described a preferred formo! my invention in connection with electrolytic condensers, it is to be understood that various modiiications and changes can be made within the Vflied July 20, 1935.

scope andv spirit of my invention. My containers and cathodes and my method of producing con- 1 tainers and cathodes can be applied to other types I claim:

l. A method of treating the surfaces of hollow containers adapted to be employed as cathodes for electrolytic condensers and the like comprising spraying the inside surfaces of the container which come into contact with the electrolyte with nnelydivided particles of molten metal to deposit a protective and conductive layer on said surfaces.

2. A method of making cathodes for electrolytic condensers and the like comprising forming a hollow container for electrolyte of material cob Ill rodable `by the electrolyte, and spraying the inside surfaces of the' container which come into contact with the electrolyte with nnely divided plastic particles o f a metal which is not corroded Aby the electrolyte thereby producing a protective y and conductive layer of metallic particles on said surfaces.

3. A method of making cathodes for electrolytlc condensers and the like comprising forming a hollow container for electrolyte of aluminum, and spraying at least a portion of the inside surfaces of the container which come in contact with the electrolyte with nely divided plastic particles of copper thereby producing a porous protective and conductive layer of copper on" said surfaces.

4. 'Ihe method of protecting the surfaces of)` cathodes of electrolytic condenserswhlch com prises depositing on the surfaces of the cathodu which are exposed to the electrolyte a layer of nnely divided particles of molten metal which adhere to the cathode and cohere toeach other to provide a porous conductive layer having a A large superncial area.

5. A method of providing a surface for cathodes of electrolytic condensers which consists in spraying a base of nlm-forming metal with finely divided plastic4 particles of copper, thereby providing ythe cathode with a porous, protective and conductive coating of copper. having a large superncial aresfadaptedtobeexposedtothe elec- 

